Material injecting method and material measuring apparatus in injection molding machine

Abstract

An injection molding method operable in conjunction with an injection molding machine having an injection screw which rotates and moves backward while a preset dosage of molding material is injected into the molding machine. As the injection screw moves backward its arrival at a predetermined point relative to a discharge nozzle is detected by a sensor which initiates stoppage of feeding of material into the machine. Further backward movement of the injection screw resulting from internal pressure in the injection cylinder is arrested by an adjustably locatable stopper, disposed behind the injection screw. The stopper is designed to be located at a position that produces molded products of consistent quality. Further, in accordance with a preferred embodiment of the invention, the stop position of the injection screw is also used as a starting point for the injection screw in a subsequent injection step during which the dosage of material is injected into a molding cavity.

What is claimed is: 
     
       1. A method for controlling a dosage of injected material in an injection molding machine, comprising the steps of: feeding a material to be injected into the injection molding machine;   enabling an injection screw of the molding machine to rotate and move backward away from a discharge nozzle of the injection machine to set the size of the dosage of material;   providing a measurement completed sensor, detecting the arrival of a predetermined portion of the injection screw at the sensor and terminating feeding of the material responsive thereto;   locating a variably positionable stop position means of a stopper means at a selected location relative to the injection screw in a manner that is effective to stop backward movement of the injection screw at a stop position, subsequent to the arrival of the injection screw at the sensor, the stop position means being movably locatable relative to the injection screw along an axial path, anywhere between two end positions on the axial path; and   stopping backward movement of the injection screw at the stop position by actuating the stopper means.   
     
     
       2. The method of claim 1, further comprising injecting the dosage of material into a molding cavity and employing the stopped position of the injection screw at the stopper means as a starting point for the injection screw during the injecting step. 
     
     
       3. The method of claim 2, further including preadjusting the location of the variably positionable stop position means prior to starting of the feeding step in order to set the quality of product obtained from the method. 
     
     
       4. An injection molding machine, comprising: an axially extending injection cylinder having front and rear regions, a discharge nozzle at the front region and a charging hole axially spaced rearward of the discharge nozzle;   a rotatable and axially movable injection screw in the injection cylinder, the injection screw being movable backwardly away from the discharge nozzle and having a detectable member that moves together with the injection screw;   means for feeding a material to be injected into the cylinder;   a sensor located at a predetermined position in the vicinity of the rear region of the cylinder, the sensor being effective for detecting the arrival of the detectable member thereat and means for terminating the feeding of the material responsive to said detection; and   a stopper means, disposed generally rearward of the injection screw and including a variably postionable stop position means.   
     
     
       5. The injection molding machine of claim 4, in which the stopper means comprises a guide rod parallel to and spaced from the injection screw, a leg securely coupled to the injection screw for movement therewith, the leg moving along said guide rod, and wherein the stop position means includes a stopper member movably locatable at a desired location on the guide rod and effective for engaging the leg and for arresting backward movement of the injection screw. 
     
     
       6. The injection molding machine of claim 5, further comprising a first detector for initiating injection pressure in the injection molding machine, the first detector being spaced away from the sensor axially toward the discharge nozzle. 
     
     
       7. The injection molding machine of claim 6, further comprising a second detector for detecting arrival of the leg at the second detector and for initiating stoppage of the injection cycle in the molding machine, the second detector being spaced axially from the first detector toward the discharge nozzle. 
     
     
       8. The injection molding machine of claim 4, wherein the stopper means comprises a screw shaft mounted parallel to and spaced from the injection screw, a leg mounted to the injection screw and mechanically coupled to the screw shaft in a manner which causes the screw shaft to rotate as the injection screw moves forward and backward in the cylinder and a braking device for braking the screw shaft and thereby stopping backward motion of the injection screw, and wherein the stop position means includes a movable position detector locatable at a desired position for detecting the leg on the injection screw and for actuating the braking device. 
     
     
       9. The injection molding machine of claim 8, wherein the braking device comprises an electromagnetic brake. 
     
     
       10. The injection molding machine of claim 9, further comprising an electric servo-motor for operating the electromagnetic brake.